This is what APOD suggested for MPA Stirlings
Minimum at maximum range 2000lb. This is the Sunderland gross load and that was normally eight-250lb Mk XI DC. This was a modified Mk VIII with a concave nose to reduce ricochet, and this was the standard airdropped DC from 1942.
OK, the normal Stirling bomb bay was built for seven 2,000lb bombs in the main bay OR eighteen 500lb bombs in the fuselage and six in the wing bomb cells.
Now the 500lb GP bomb was 12.9" x 71". The Mk VII DC (ship dropped) was 17.65" x 27.8", add a pointy end and a draggy end... and it is probably still too fat! Redesigning the wings is probably not do-able so we are stuck with 250lb DC in those cells with their 170lb amatol charges. That's OK, we can put Mk VII (290lb amatol) in the bomb bay and then we have big bangs in the centre of the pattern and the 250's still extend the coverage of the pattern nicely anyway.
OK, I want the wing cells. Six-250lb Mk XI DC. That gives me three attacks.
This is nice because of the Stirling wing cells, into which the 250lb DC fits. This would give two really nice patterns of four DC each with something all other acft lacked, both centreline laid DC and a side offset.
The wing bomb cells would otherwise be nice fuel tanks, but they are very small and to be blunt you'd be better off with a huge tank in the bomb bay, reducing its size overall.
But as it was built for 2000lb bombs (actually a 1900lb bomb), which was 19" wide, it will take 500lb Mk VII!
I already have three attacks maximum, which is a lot, so I want six Mk VII. And just because I like MPA guys (my father's cousin was one with 10 SQN), another 3 gives them options to really make a U-boat's life really exciting. Not to mention brief.
So I want the wing cells (6 x 250lb Mk XI) and nine-500lb Mk VII.
Now it gets more interesting. I only need half the weight capacity of the wing cells but all of their volume. But I have still liberated 1,500lbs of weight from the wings.
I also do not need half of the bomb bay weight. So that liberates 4,500lb of weight from there. There will be a bit more because there is structure (shackles etc) I now do not need. That's 6,000lb freed up... to devote to more fuel.
I'd also like at least a lick and a promise to U-boat flak suppression. I'd REALLY like two .50cal in the nose turret. The .50 cal can reach out and touch someone. I'd really, REALLY like a pair of 20mm there to reach out and touch someone at longer range.
We can lose the dorsal turret. Due to CG reasons we can't lose the tail turret and a tail turret is a seriously useful place to have a pair of eyes and 4 x .303 will suppress the hell out of a U-boat's flak for the second and third attacks. I now need that tail turret, it buys me tactical options.
I want two observation blisters aft port and starboard for more eyes and I also want two bunks, a tea urn and a hotplate with a small table seating 2. This beast is going to be doing long sorties and that buys me a new world of fatigue management. I want to be able to get people rested in rotation.
There is basically no fighter threat, these boys won't be messing about close in over Biscay because we have Sunderlands and Blackburn Nutcrackers for that, they will be deep Atlantic specialists
Much wailing and gnashing of teeth from Bomber Harris. The kicker is that he has a certain inventor's high-altitude geodetic super-bomber, the Vickers Victory, entering service now to take the burden off the current and definitely dodgy RAF high altitude bomber (Wellington Mk V), and an even bigger, better, badder high flyer, the six-Centaurus powered canard Vickers C under feverish development. OK, it will probably be too late for Germany but when that beastie flies into the first USAAF Pacific B-29 base and all of a sudden makes the B-29 a medium bomber it should impress the heck out of the Japanese.
SO production will be ramped down and it will become Coastal Command's new MPA, for which it is actually very well suited because Shorts designed it. It's altitude restrictions do not matter, and its exceptional manoeuvrability at low altitude is a real boon.
The production capacity released will go into the Lanc/Manchester production, I guess. Manchester with the fixed Vulture engine (Shane christened it 'Bustard'. Ahem.) is the el-cheapo Far-east heavy bomber. it is good enough.
Ok I just happen to have discovered my pilot’s notes for the Stirling, and no you can't have the wing cells on the VLR variant.
There's 438 galls of juice there, that’s an hour's flight at MAX RICH continuous, almost 2 hours at 5,000' on weak mixture @ 2,400rpm +2lb boost on 100 octane (flat chat cruise for the Herc VI). You no getty that - greedy man.
To cut a long story short we have 2,254 galls in the wings, + 438 in the wing bomb cells for 2,692 galls all up with no FFO mods.
Flight profile
Climb to 5,000' and cruise @ 160 mph all the way out and back, on Herc VI.
Climb @ 70,000lb - 20 miles, 50 galls
2,672 left
Cruise @ 65,000lb, 5k' 160mph, 2,300rpm = 228 gph
2672 - 10% reserve = ~2,400 galls
2,400/228 = 10.5 hours
10.5 x 160 = 1680 air miles -> op radius is 840 air miles.
This is conservative, aircraft in BC trim, all numbers rounded down, it takes no account of reducing weight and it's all still air conditions. This is presuming I'm reading the tables correctly.
How much more do you want Mark?
On the bow guns, I think you're going to have to be content with a pair of .303 Browning’s until 43-44, the mid upper I though we might retain for Biscay bombers, but strip off for the Gap fillers.
Nope. I want the wing cells because that is what the OR blokes will want.
Looking roughly at the numbers, I think that adding the wing cells with their 170lb of burster increases the U-boat kill percentage from a single stick of 4 Mk VII DC by roughly 60-80% by adding 4 Mk XI. This is a very serious point and Coastal Command (they invented operational research evaluation) will make this point long and loud. Those wing cells make the Stirling the deadliest MPA in the sky, no joke.
1 gal is about 6.5lb of fuel. So I'll swap the 438 gallons of juice there for about 923 gallons of juice in the bomb bay. That's roughly 3180 gallons for a 13.7-hour sortie.
This aircraft, now about 60-80% more effective in attack than a Wellington, is already looking exceptional.
Now we feather one engine on the transit legs and cruise merrily on about 80% of that fuel consumption...
It adds up fast.
Agree that the Mk I MPA will be a BC standard with a paint scheme and different radios. But that is just the start of the mod path. Trust me on this one, the pattern you get with those wing cells makes a significant difference. If you really, really want them for range, the two inners could go, but I do not see the need.
How about we keep the wing cells as is, and leave tankage or DC's as an open option for flexi ability’s sake? It's not like there's any extra work involved either way.
Remember OR is but a newborn babe at this point. The Certainty and Influence of their conclusions in 42-3 isn't up to 44-45 standards. Hell it's a nice little data point for them study.
Agree. Leave them as is and you buy all sorts of mission flexibility and tactical options at no cost.
This means you could do a max fuel load option for extreme range, and carrying even 4 Mk VII out an additional day's steaming (250nm), to get a plane over a convoy saves ships.
Yes, ORE was new at this stage, but it was getting on its feet and aircrew were working on more efficient patterns themselves. The Wellington experiences in western approaches were where that came from. The critical lesson of 1917-18 had been learned by the CC men by this stage, that while sinking U-boats was nice and earned medals, saving ships from being sunk was what it was all about.
Stirling already had slot-in tanks for the wing cells. It would be a minor job to develop slot in tanks for the bomb bay rather than one big, permanent fitting. Yes, more pumps etc are needed, but in the first series of mods to start turning Stirling into the longest-ranged MPA, possible, I think that the removal of the dorsal turret will occur, and they will buy the needed weight.
Stirling will be a very good MPA, it is strong and has excellent performance at low altitudes, and can be modified for more range. Above all, in the free-fall A/S weapon era, it has a built-in 'edge' in combat effectiveness. The wing cells really do make a difference. I suspect it would serve post-FFO well into the 60s.
Transit would be at a cruising altitude where maximum time on station over the convoy would be wanted. An alternative to this would be a low-level radar search patrol using ASV out to a closer convoy, doing a partial search of its track. Altitude for radar and visual search would be 4000-5000' depending on weather. Visual/radar search altitudes would be 2000-5000' depending on weather. In bad weather, the MPA might be bucking along at 300' just under the cloud base, for example. In clear, calm conditions, you really can see a periscope feather from 5000' when it is 5 miles away.
For distant convoys, a 3-engine transit at economical speed and altitude would be the norm, with ASV turned off to save it for sweeping the water around the convoy. Probably (unless the convoy was under attack), the MPA would sweep the convoy itself to look for trailers and then work ahead, beating the sea with both radar and visual search 5-50 miles ahead. They would make sure to come back over the convoy every couple of hours to check again for trailers and for morale. Nothing helped morale more than seeing the MPA when convoys were in tiger country. The impact was striking, fewer stragglers and rompers, for example.
